This example sets up an OSPF network at a small office. There are 3 routers, all running OSPF v2. The border router connects to a BGP network.

All three routers in this example are FortiGate units. Router1 will be the designated router (DR) and router2 will be the backup DR (BDR) due to their priorities. Router3 will not be considered for either the DR or BDR elections. Instead, Router3 is the area border router (ASBR) routing all traffic to the ISP’s BGP router on its way to the Internet.

Router2 has a modem connected that provides dialup access to the Internet as well, at a reduced bandwidth. This is a PPPoE connection to a DSL modem. This provides an alternate route to the Internet if the other route goes down. The DSL connection is slow, and is charged by the amount of traffic. For these reasons OSPF will highly favor Router3’s Internet access.

The DSL connection connects to an OSPF network with the ISP, so no redistribution of routes is required. The ISP network does have to be added to that router’s configuration however.

This section includes the following topics: